Infected patient in quarantine lying in bed in hospital, coronavirus concept.

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PARIS — Although new information emerges about COVID-19 nearly every day, there is one thing scientists have been saying since the very beginning of the pandemic – it’s not the flu. A new study confirms this important distinction through a comparative analysis of risk factors, clinical characteristics, and outcomes in hospitalized patients with COVID-19 or seasonal influenza.

The study, published in The Lancet Respiratory Medicine, compares data collected from COVID-19 patients over a two-month period from March to April, 2020 and patients with severe influenza over a three-month period during the 2018/2019 influenza season. The data were collected using the French national administrative database which includes discharge summaries for all hospital admissions in the country.

During the study periods, 89,530 patients were hospitalized for COVID-19 and 45,819 patients were hospitalized with influenza. That’s nearly twice as many patients admitted for COVID-19, over a shorter time period.

The authors suggest that immunity to influenza, either as a result of vaccination or previous infection, could account for some of the differences seen in hospitalization rates. Since SARS-CoV-2, the virus responsible for COVID-19, has never been seen before by humans, there is no preexisting immunity in the population. Nevertheless, the authors emphasize that the potential for respiratory complications in both diseases highlights the importance of all physical measures of prevention, especially with the impending threat of a COVID-19 and influenza “twindemic.”

COVID-19 is much deadlier than the flu

One of the most notable observations of the study is regarding death rates. The study finds that COVID-19 patients are almost three times more likely to die than patients hospitalized for influenza (16.9% vs 5.8%).

“Our study is the largest to date to compare the two diseases and confirms that COVID-19 is far more serious than the flu. The finding that the COVID-19 death rate was three times higher than for seasonal influenza is particularly striking when reminded that the 2018/2019 flu season had been the worst in the past five years in France in terms of number of deaths,” says study co-lead author, Catherine Quantin in a statement.

According to the study, hospitalized COVID-19 patients are more likely than influenza patients to experience a severe illness requiring intensive care (16.3% vs 10.8%). Moreover, the average length of stay in the ICU for COVID-19 patients is nearly twice as long (15 days vs 8 days). If admitted to the ICU, COVID-19 patients are more likely to require invasive mechanical ventilation than patients with influenza (9.7% vs 4.0%). Acute respiratory failure, or the inability of the lungs to get oxygen into the body, is also more common in COVID-19 patients (27.2% vs 17.4%).

Overall, patients with COVID-19 in this study have fewer underlying medical conditions than those with influenza. In agreement with what has been reported in other studies, COVID-19 patients are more often to be overweight or obese, or to have high blood pressure or diabetes. Heart failure, chronic respiratory disease, and cirrhosis, although frequently associated with COVID-19, are more often observed in the patients with influenza.

“Thus, although the differences in comorbidities might explain the difference in disease severity, the difference might also be due to an exaggerated immune response in COVID-19, or due to the exacerbation of comorbidities in influenza infection,” the authors write.

‘Findings clearly indicate that COVID-19 is much more serious than seasonal influenza’

The study finds that children under the age of 18 appear to have a lower risk of being hospitalized for COVID-19 than for influenza (1.4% vs 19.5%). However, the death rates of those children are more than four times higher than for children with influenza. The authors note that this is in contrast to recent reports stating that COVID-19 is often mild in children.

The authors mention several limitations to their study, including variable practices for influenza testing across hospitals versus more standardized testing for COVID-19. Additionally, the 2018/2019 flu season may not be representative of all flu seasons. The authors note, however, that it was the most severe season in France in the past five years.

“Taken together, our findings clearly indicate that COVID-19 is much more serious than seasonal influenza. At a time when no treatment has been shown to be effective at preventing severe disease in COVID-19 patients, this study highlights the importance of all measures of physical prevention and underlines the importance of effective vaccines,” study co-lead author, Pascale Tubert-Bitter said in a statement.

About Judy Minkoff, PhD

Judy Minkoff holds her doctorate in immunology and molecular pathogenesis from Emory University. She has over a decade of experience in preclinical laboratory settings working on viruses and vaccine development. She was a medical writer for two-and-a-half years and has been a freelance science writer and editor since 2016.

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